Method of concentrating fluorspar ores



United States Patent 3,207,304 METHOD OF CONCENTRATING FLUORSPAR ORESClarence Thom, Denver, (3010., assignor to The Dow Chemical Company,Midland, Mich., a corporation of Delaware Filed Nov. 15, 1962, Ser. No.237,818 2 Claims. (Cl. 2099) This invention relates to an improvedmethod of recovering fluorspar ores and more particularly to an improvedfroth flotation process including a more economical depression andseparation of calcite, quartz, metal oxides and other calcareous andsiliceous gangue minerals with which fluorspar is generally associated.

The generally accepted method of the prior art comprises the pre-mixingof the ground ore with water and certain flotation agents, a stepreferred to in the art as conditioning, for various lengths of timeafter which the conditioned pulp is subjected to flotation to produce afroth concentrate of the valuable fluorite minerals and a non-floatingproduct containing the undesirable impurity minerals which are discardedas waste failings. These prior art methods also require control of thepulp temperature and the addition of substantial amounts of heat torender the reagents more effective. Additionally, these processesrequire the removal of practically all of the soluble hardness formingsalts from the water used in the process.

The conditioning is usually accomplished in an agitation tank whichreceives the ground ore pulp at a specified water to solids ratio, thewater having been previously softened. The heating of the reagentizedpulp in the conditioner tank or in the flotation machine is generallyaccomplished by means of the injection of live steam or by means ofexternal heating units.

The costs of water treating and heating of the pulp in these prior artprocesses are undesirably high and are therefore wasteful. Further, thegeneral practice of the depression of the impurity minerals at thealkalinity desired in the flotation operation and in the presence of thealkaline reagents in the pump is considered both wasteful and expensive.

Contrary to prior art teachings, it has been found that the separationof fluorite from impurity minerals by flotation and, more particularly,the separation of fluorite from calcite and siliceous impurity mineralscan be more effectively accomplished when the conditioning of the pumpis carried out at a lower degree of alkalinity than is necessary for thesubsequent flotation.

Further, in contrast to the prior art methods, the method of the instantinvention does not-require the addition of heat to the slurry under thenovel conditions of operation. Also,fewer flotation cells are requiredto eifect efficient recoverysince the flotation is more rapid andcomplete and the depression of the calcite is also more positive andcomplete than in prior art processes.

In accordance with the invention, the improved method of concentrating afluorspar ore comprises the steps of comminuting the ore, forming anaqueous slurry of the comminuted ore, adding a depressant reagent forimpurity minerals to the slurry, conditioning the slurried ore at alower alkalinity than that required for subsequent flotation offluorite, raising the alkalinity of the conditioned ore slurry, adding acollector reagent thereto and subjecting the resulting slurry toflotation in order to recover the fluorite values as acid gradefluorspar.

It is an important object of the present invention to provide animproved method of concentration of fluorspar from ores containingimpurity minerals by means of which acid grade fluorspar can becommercially produced with greater economy both in reagents and heatrequirements.

A further important object of the present invention is to provide animproved method of concentrating fluorspar ores containing impurityminerals in which the ore conditioning step is carried out at loweralkalinities than that considered essential for a subsequent flotationstep.

Another object of the present invention is to provide an improved methodof concentrating fluorspar ores at temperatures which ordinarily do notrequire the addition of heat to the system.

Another object of the present invention is to provide an improved methodfor the concentration of fluorspar ores containing impurity minerals bymeans of which acid grade fluorspar can be commercially produced withoutrequiring complete water softening of water used in the process.

A further object of the present invention is to provide an improvedmethod for the concentration of fluorspar ores containing impurityminerals which is more efficient and economical than processes usedheretofore requiring substantially less flotation equipment for the sameore treating capacity.

Another and further important object of the present invention is toprovide an improved method for the concentration of fluorspar orescontaining impurity minerals wherein the alkalinity of the pulp water iscontrolled in the conditioner and raised in the flotation machines.

A still further object of the present invention is to provide animproved method for the concentration of fluorspar ores containingimpurity minerals which includes the step of pre-conditioning the orepulp in the conditioner with an impurity depressant reagent before theaddition of promoter reagents and pH modifying agents.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

In the drawing, the sole figure is a self-explanatory flow diagram of afluorspar concentrating process according to the invention.

It has been discovered that a more economical depression and separationof calcite, quartz, metal oxides and other calcareous and siliceousgangue from fluorspar ores can be made, and at lower than normaltemperatures, provided the pulped ore is pre-conditioned with animpurity depressant reagent at an alkalinity less than flotationalkalinity prior to the introduction of promoters and pH modifyingagents.

It is a standard in the prior art that the depression of impurityminerals in the concentration of fluorspar ores is invariablyaccomplished at the alkalinity desired in the flotation operation and inthe presence of the alkaline agents in the ore pulp. It is discoveredthat this is not only wasteful of reagents but also adversely affectsthe recovery of the values.

It has also been discovered that the lowering of the alkalinity in theore pulp may be accomplished to advantage by pre-conditioning the pulpin the presence of acid forming salts which may exist to a certaindegree proportionally to the hardness of the natural water used in theprocess which also removes the usual requirement that the water used becompletely softened. On the other hand or in addition, the acidityrequired for lowering the alkalinity of the pulp may be obtained by theaddition of mineral acids or certain acid forming salts to the ore pulp.Another very convenient method of achieving the lower alkalinity is theuse of an acidulating depressing agent such as quebracho or othercalcite depressing reagent which contains an amount of tannic acid toeflect all or part of the lowering of the alkalinity of the pulp to thedesired level.

As shown in the drawing, the fluorspar ore is crushed in crusher 1t),mostly to 100 mesh. The crushed ore is fed into a wet grinding circuitincluding grinder 12. The crushed ore is slurried with water which mayhave hardness forming salts present not in excess of about 80 parts permillion. Some softening of the water used, may be required for watenshaving hardness in excess of this figure. The ground ore slurry passesto a classifier 14, where the +100 mesh ore is returned to the grinder.The 100 mesh ore slurry at about 25% solids is fed to the conditioner16. The pH of the ore pulp in the conditioner is adjusted to analkalinity less than the alkalinity of the ore to be used in thesubsequent flotation operation. The alkalinity ditference may be asgreat as several tenths of a point of pH to as little as one tenth of apoint depending on the particular ore, water and the like. These pHadjustments may be accomplished by or in addition to the adding of adepressant reagent. The addition of a depressant of acidic nature suchas quebracho may provide all or part of the adjustment required. Otheracidulators such as mineral acids or acid forming salts may be added toadjust the alkalinity of the ore pulp. The temperature of the pulp inthe conditioner is maintained above about 70 F. with the injection ofsteam being required only when necessary to maintain the temperature.Usually, the addition of heat will be required only during the coldestparts of the year to maintain the operating temperature in this range.

After the pulp is conditioned for a time suflicient to depress theimpurities, the alkalinity is then raised to the flotation pH by theaddition of an alkaline reagent, such as, soda ash and the like and atthe same time the promoter o-r collector agent, such as oleic acid, isadded. The flotation and pH control agents are added after theconditioner, either in or just ahead of the first rougher cell. The pHof the pulp in the rougher 18 is adjusted to be in the range of from asmuch as several tenths of a pH point to as little as one tenth of a pHpoint higher than in the conditioner.

The overflow from the rougher 18 is fed to the cleaner 20 and theunderflow goes to the tailings. The pH in the first cleaner cell may beslightly less alkaline than in the rougher and a pH slightly lessalkaline than this is usually suitable for the remaining cleaner cells.

The overflow from the cleaner goes to thickener 22 and the underflow totailings. The thickener underflow is de-watered in filter 24 and driedto provide an acid grade fluorspar. The over-flow from the thickener andfilter is returned to the grinding circuit.

As an example of the operation of the present invention, a typicalfluorspar ore having the following general composition shown in Table Iwas used.

TABLE I Wt. percent CaF 77.0 CaCO 15.0 Quartz 5.0 R 3.0

4; Example 1 The raw ore was sent to a jaw crusher, to a cone grinderand finally to a ball mill where it was mixed with water and groundmostly to mesh. The water used was settled and softened until itcontained from 20-80 p.p.m. hardness. The slurry of ore and water passedfrom the ball mill to a hydraulic cyclone classifier which providesabout a 25% solids slurry of 100 mesh as feed and returns the underflowto the ball mill. The feed slurry from the hydraulic cyclone is passedto an agitated conditioner provided with steam jets for regulating thetemperature in the conditioner.

According to the improved method of this invention, the 100 mesh pulpwas fed to the conditioner at a pH of about 7.8 to 8.4. In theconditioner 0.170 kilogram of quebracho per metric ton of ore is addedto the pulped ore which is maintained at about 77 F. Nothing further isadded to the conditioner and the conditioner pH is about 8.08.2. Theslurry from the conditioner is treated with 0.386 kg./m.t. of soda ashand 0.270 kg./m.t. of oleic acid as it enters the first rougher cell.The pH in the first rougher cell is 8.4-8.6. In the rougher cells thefluorspar floats to the top with the froth and the gangue falls to thebottom and is discarded. The froth from the rougher cells flows througha launder to a four stage cleaner circuit that further separates thefluorspar and the gangue. The fluorspar concentrates are sent to athickener where the fluorspar settles. The thickened concentrate isde-watered to an 84-88% solids by filtration and dried. The recovery ofCaF was found to be 85.6% which analyzed 97.5% CaF Example 2 An orehaving the composition of Table I was comminuted, classified andslurried with water having the same hardness of Example 1. The pulpedore was introduced into the conditioner and maintained at about 77 F.,however, the depressant reagent queblracho in the amount of 0.170kg./m.t. and the promoter and pH control reagents in the amount of 0.270kg./m.t. of oleic acid and 0.386 kg./m.t. of soda ash were all added tothe conditioner simultaneously. The thus conditioned pulp passed throughthe balance of the circuit in the same manner as in Example 1. Therecovery of acid grade CaF was 70%.

Example 3 An ore having the same composition was comminuted and slurriedwith a water softened to 20-40 p.p.rn. hardness. The slurried ore wasconditioned as in Example 2 at a pH of 9.0-9.6 except the temperaturewas increased to F. The pulp passed through the remainder of the systemin the standard fashion and 67.3% of the CaF was recovered whichanalyzed 98.3% CaF In Examples 2 and 3 where the conditioning of the oreslurry occurred in the presence of the promoter and pH control reagents,a lower percentage recovery was realized; whereas, in Example 1, wherethe conditioning was accomplished at a pH less alkaline than thatconsidered practical for the subsequent flotation operation and in theabsence of the promoter and pH control reagents, and the alkalinity wasincreased for flotation by the addition of the promoter and pH controlafter the conditioning step, the percentage recovery is significantlyincreased.

While there have been described what at present are considered to be thepreferred embodiments of this invention it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention. It is aimed, therefore, inthe appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

What is claimed is:

1. In a process of concentrating fluorspar ore by firoth flotationincluding the steps of comminuting and pulping the ore with water,pre-conditioning the pulped ore, adding a collector reagent to said oreand subjecting the pre-c0nditioned ore to a flotation operation torecover the fluorspar values, the improvement which comprises:pre-conditioning the pulped ore for a period of time with an acidulatingdepressing agent while maintaining the temperature above about 70 F.said acidulating depressing agent being further characterized ascontaining an amount of tannic acid sufficient to efiect a lowering ofalkalinity of the pulp to a level of at least 0.1 pH unit below theflotation alkalinity required in the subsequent flotation operation. 2.The improvement in accordance with claim 1 wherein said acidulatingdepressing reagent is quebracho.

References Cited by the Examiner UNITED STATES PATENTS 2,168,762 8/39Clernmer 209-166 2,263,552 11/41 Anderson 209-166 2,407,651 9/46Clernmer 209166 2,410,770 11/46 Booth 209-166 2,825,45 8 3/58 Snyder 209166 FOREIGN PATENTS 1,118,112 2/60 Germany.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

1. IN A PROCESS OF CONCENTRATING FLUORSPAR ORE BY FROTH FLOTATIONINCLUDING THE STEPS OF COMMINUTING AND PULPING THE ORE WITH WATER,PRE-CONDITIONING THE PULPED ORE, ADDING A COLLECTOR REAGENT TO SAID OREAND SUBJECTING THE PRE-CONDITIONED ORE TO A FLOTATION OPERATION TORECOVER THE FLUORSPAR VALUES, THE IMPROVEMENT WHICH COMPRISES:PRE-CONDITIONING THE PULPED ORE FOR A PERIOD OF TIME WITH AN ACIDULATINGDEPRESSING AGENT WHILE MAINTAINING THE TEMPERATURE ABOVE ABOUT 70*F.SAID ACIDULATING DEPRESSING AGENT BEING FURTHER CHARACTERIZED ASCONTAINING AN AMOUNT OF TANNIC ACID SUFFICIENT TO